The present invention relates to a wiring system for electrically controlled devices, such as domestic cooling apparatus, flat irons, grillers and so on, and particularly for water heaters which are also connected to a solar system, and more particularly to the visual indication of their positive performance and/or their temperature. It is well known to provide a small incandescent lamp, usually a red one, connected to the circuit in such a manner that, by its glowing, it indicates that the device is under current, e.g. the thermostatic switch thereof, if any, is in closed position. When the circuit is broken, either automatically by the thermostat, or manually by an exterior switch, it stops glowing, announcing the breaking of the circuit.